Trendy names come and go, and so too do those androgynous names that work just as well for both girls and boys. Check out this gorgeous data visualization to see how our acceptance of these gender-neutral names have changed over the course of the past 100 years.

A name is considered unisex if there's somewhere between a 60/40 and a 50/50 split between the sexes. Names like Nancy and Julia tend to be female, while names like Brian and Joseph are almost always male. But then you've got names like Casey, Shannon, Tracy, and Jamie — names that fit within this unisex category.

Taking information from the U.S. Social Security Administration, FlowingData's Nathan Yau plotted the popularity of these gender-neutral names from 1930 to 2012. He created charts for the top 35 unisex names and the percent of babies with unisex names over time (both can be seen here).

The top five unisex names in U.S. history are Jessie, Marion, Jackie, Alva, and Ollie (in that order).

He also created a chart showing how the names have shifted in and out of of their unisex status and popularity over time. The above graph (click to make it bigger) goes by count and a simple percent threshold.

So, for example, the Taylor spike in 1992 indicates a dramatic shift from a mostly male name to a mostly girl's name (for unknown reasons — anyone have a clue?).

Yau writes:

Jessie, Marion, and Jackie top the list, as they've stuck around that 50-50 split over the decades. Of course, as you move down the list, there are more slopes up and down and some noisy spikes for the less common baby names, such as Gale and Alva.

For trendy (and poisoned) names, the results are more easily explained. There's often a direct cause — an event, actor, movie, or song — that triggers a spike or a dip. The unisex explanations are less straightforward. There are subtle spikes like when Marion Jones won gold in the Olympics (and eventually lost them), when Jackie Robinson entered the major leagues, or when Disney named their mermaid Ariel, but the changes are for the most part gradual. A name slowly becomes more male or female. Most unisex names only stay that way for a few years.